1. Field of the Invention
The present invention relates to a method of soldering an electric cable to an electronic circuit board directly and, particularly, to a soldering method with using a heater chip of a heated soldering device.
2. Description of the Prior Art
In a case where an electric cable such as flat cable is soldered to an electronic circuit board, it is usual to directly solder core conductors of the flat cable to a wiring pattern on the electronic circuit board. In such case, however, a portion of a coating of the electric cable in the vicinity of soldered portions is melted by soldering heat and the corresponding portion of the core conductors to the melted coating are exposed. As a result, mechanical strength of the core conductors in the vicinity of the connecting portions is degraded, leading breakage of the conductors.
In order to solve the problem of breakage of the conductors around the soldered portions, an electric cable protecting method is disclosed in Japanese Patent Application Laid-open No. Sho 60-95869 published on May 29, 1985, in which a hot-melt of a plastic material which becomes a molten state by heat and then solidified is fixed on a tip portion of an electric cable. The hot-melt is melted by heat given to the solder connecting portion of the electric cable, flows to a peripheral portion of core conductors of the cable to fill it and, then, is solidified. With such hot-melt, the core conductors around the connecting portion is reinforced and the conductor breakage is prevented.
In this method, however, there is a problem that a molten hot-melt flows onto a surface of the circuit board, so that the board surface is contaminated. Further, since it is impossible to control the flowing direction of the molten hot-melt, there may be another problem that hot-melt adheres to undesirable portions of the circuit board which are not to be covered by such hot-melt.
On the other hand, when an electric cable is to be soldered to a circuit board by utilizing a heater tip of a heated soldering device, there is a problem that solder dregs remain on the heater tip, leading to defective soldering. Therefore, the heater tip must be cleaned frequently.